The present invention generally is related to electrical machines, especially motors, and more precisely to a method of producing an armature segment of an electrical machine, which armature segment includes a coil and a core section.
Electrical machines work by the interaction of magnetic flux and current. At operating limits the magnetic flux is limited by saturation of the soft magnetic material and the current by the temperature resulting from ohmic heating. If more space is provided for conductors to reduce current densities and hence ohmic heating, the magnetic flux is also reduced and vice versa if more soft magnetic material is included the flux is increased but the conductor area is reduced and ohmic heating increased.
In most machines the conductors are contained in slots. It is necessary to semi-close the slots to obtain a smooth torque output and the result is that placing the windings in the slots is a difficult task which results in a poor ratio of conductor area to slot area. Ratios in the region of 50% are considered good. This poor ratio is bad for two reasons, firstly space is wasted which could be used for conductor or soft magnetic material and secondly the space in the slot will act as a thermal barrier increasing the temperature for a given ohmic loss.
By integrating the coils of an armature in the body thereof, it should be possible to increase the ratio of conductor area to slot area in other applications, it is known to integrate a coil into a body made of compressed metal powder, Thus, SE-A-9501500 discloses a magneto-strictive sensor having a housing made of metal powder and a sensing coil integrated therein.
An object of this invention is to provide an armature, preferably a stator, for an electrical machine which armature has a better ratio of conductor area to slot area than armatures in the prior art.
A method of producing an armature segment of an electrical machine, which armature segment includes a coil add a core section in accordance with the present invention is characterised by the features specified in the appended claim 1. Preferred embodiments of that method are defined in the dependent claims.
Thus, this invention is concerned with first producing tightly wound coils. Then each tightly wound coil is placed in a die where it is compacted for shaping the tightly wound coil so that the cross-sectional area of the tightly wound coil is reduced. Preferably, this means that the cross-sectional shape of each wire of the coil is deformed toward a hexagonal shape. Thereafter, the compacted coil is positioned in a die for compaction of insulated iron powder to form an integrated coil and core unit. The armature of the machine is then assembled from a number of these units.
The coils being produced away from the geometric difficulties of insertion into the slots can have a far higher ratio of copper to slot area; using machine winding 70% is easily achieved. By the further step of compressing the coils in a die 81% can be achieved which is getting close to the theoretical maximum (which is fixed by the need for insulation around the conductors).
The result of this high ratio of conductor to slot area is a major reduction in coil resistance and excellent thermal conduction properties. At the same time, these coils may easily be produced using simple bobbin winding technique using fully automated techniques which are not expensive to implement.
The compaction of the insulated iron powder with the previously compacted coil produces a finished component, thereafter only requiring a heat treatment before assembly with the other components. Another benefit of the compaction is excellent thermal contact between the core and the coil allowing high currents densities to be used and higher output to be achieved from the same material.